Facial and body whiskers serve as a remarkably sensitive source of tactile information for many species of mammals. For example, harbor seals can use their facial whiskers to track hydrodynamic trails, an ability thought to aid long-distance prey tracking (Dehnhardt et al. 2001). As another example, behavioral experiments on rats have shown that individual whiskers provide the fine-grained distance discrimination sensitivity needed to sense aperture width (Krupa et al. 2001). Increased study of the biological function of whiskers has been paralleled by an increasing interest in constructing their robotic counterparts (see references). Robotic whisker arrays could be used in a wide variety of applications, ranging from fine sensing tasks that push the limits of tactile discrimination and hence require engineers to construct systems that rival animals' exquisite tactile sensitivity, to obstacle-avoidance tasks that require only far coarser sensing capabilities.
The simplest types of artificial whiskers are those which are used as binary contact detection sensors. These have been used on several successful toys (e.g. “BioBugs” made by WowWee/Hasbro). Other researchers have explored the use of whiskers for wall-following and to characterize surface texture and surface defects. Most recently, a whisker sensor was designed for precise three-dimensional measurement of heart position in robot assisted beating heart surgery.
An important feature of biological whiskers is their ability to extract three-dimensional (3D) features, either of solid objects or of fluid flows. However, few studies have investigated how this capability might be replicated in an artificial whisker array. One of the most successful approaches towards 3D feature extraction was taken by Kaneko et al., in IEEE, Trans. Robotic Autom, 14, 278-29 (1998). These authors employ a method in which a flexible beam is rotated a small amount (“tapped”) against an object while measuring bending moment at the base of the beam (whisker) to determine contact distance based on the rotational compliance. However, this method has serious drawbacks: it requires multiple adjustments of actuator orientation to keep the beam oriented perpendicular to the object, to avoid lateral slip, and also requires multiple rotations for each radial distance extraction. These are not only awkward in practice, but also infeasible when arrays of multiple whiskers are employed to contact the object.
There are two interrelated problems that have as yet prevented artificial whiskers from being used in large, highly parallel, actuated arrays to sense object features. The first problem, as mentioned above, is lateral slip, in which the whisker slides out of its primary plane of rotation. The second problem is closely related to lateral slip, and involves the need to obtain a reasonable estimate of the coefficient of friction. The invention described herein is advantageous to overcome these problems and to provide and the ability to quantify and passively accommodate for lateral slip of a moving whisker in the presence of friction.